Caucasians who have had a good deal of sun exposure in childhood will show the following gross cutaneous alterations in adult life: wrinkling, leatheriness, yellowing, looseness, roughness, dryness, mottling (hyperpigmentation) and various premalignant growths (often subclinical). These changes are most prominent in light-skinned persons who burn easily and tan poorly. The baleful effects of sunlight are cumulative, increasing with time often referred to as "photoaging". Although the anatomic degradation of the skin is most advanced in the elderly, the destructive effects of excessive sun exposure are already evident by the second decade. Serious microscopic alterations of the epidermis and dermis occur decades before these become clinically visible. Wrinkling, yellowing, leatheriness, loss of elasticity are very late changes.
Retinoids (e.g. Vitamin A and its derivatives) are substances which are known to have a broad spectrum of biological activity. Most specifically, these substances affect cell growth, differentiation and proliferation. Retinoids affect the differentiation, maintenance, and proliferation of many types of cells whether they are of ectodermal, endodermal or mesodermal origin; whether they are epithelial, fibroblastic or mesenchymal; or whether they are neoplastic, preneoplastic or non-neoplastic. At present, retinoids have found clinical utility in the treatment of severe cystic acne, psoriasis, and other disorders of keratinization. Possible uses of retinoids are being explored in the prophylaxis and treatment of cancer. For a review of developments in retinoid therapy, see Pawson, B. A. et al. "Retinoids at the Threshold: Their Biological Significance and Therapeutic Potential", Journal of Medicinal Chemistry 25:1269-1277 (1982).
The present status of retinoids in research and clinical medicine can be found in the publication of a symposium held in Geneva: J. H. Saurat. Editor, "Retinoids: New Trends in Research and Therapy," Karger Publishing Co. (1985).
It is known to use certain retinoids, particularly vitamin A acid, topically for treatment of acne as set forth in my U.S. Pat. No. 3,729,568. Other known topical uses of vitamin A acid were reviewed by Thomas, J. R., et al, "The Therapeutic uses of Topical Vitamin A Acid", Journal of American Academy of Dermatology 4:505-516 (1981) include, in addition to acne treatment, treatment of senile comedones, nevus comedonicus, linear verrucous nevus, plantar warts, pseudofollicultis, keratoacanthoma, solar keratosis of extremities, callosites, keratosis palmaris et plantaris. Darier's disease, ichthyosis, psoriasis, acanthosis nigricans, lichen planus, molluscum contagiosum, reactive perforating collagenosis, melasma, corneal epithelial abrasion, geographic tongue, Fox-Fordyce disease, cutaneous metastatic melanoma and keloids or hypertrophic scars.
It is believed that retinoids influence ultrastructural and proliferative properties of epidermal cells. However, these prior art uses of vitamin A acid have generally involved short term treatments in which relatively high concentrations retinoic acid are applied (i.e. sufficient to cause significant irritation and often peeling) in order to obtain a quick therapeutic effect of the particular condition, such as removal of comedones, as opposed to long-term treatment of normal aging or photographing skin.
My copending application Ser. No. 759,505 discloses methods for treating sundamaged human skin topically with vitamin A acid in an emollient vehicle in such amounts as to be essentially non-irritating to the skin. This treatment causes the skin, particularly human facial skin, to substantially regain and maintain its firmness, turgor and elasticity by retarding and reversing the skin's loss of collagen fibers, abnormal changes in elastic fibers, deterioration of small blood vessels, epidermal atrophy and formation of abnormal epithelial growths.